One minute after the 6:45 p.m. listed starting time for “The Hangover Part III” at the AMC Loews Boston Common, a half-full theater darkened and fell silent except for the crunching of popcorn. The ads came first. Then that familiar green light bathed rows of upturned faces.

“The following preview has been approved to accompany this feature by the Motion Picture Association of America,” flashed on the screen. Twenty minutes and seven previews later, the featured film began.

This routine, bemoaned and beloved by moviegoers, is now being debated, and at the heart of the issue is whether trailers are too long and give away too much.

The National Association of Theater Owners (yes, it’s called NATO) is asking Hollywood studios to reduce the maximum length of trailers down to two minutes, from two and a half minutes, according to a recent exclusive article in the Hollywood Reporter. Also, previews for movies that are an eternity away from being released would in most cases disappear. No more, “Coming July 2014.” Trailers would have to advertise movies that are four months off or less.

Current rules from the Motion Picture Association of America state that all trailers shown in US theaters must be no more than two and a half
minutes, except for one trailer every year from each studio that is allowed to last longer. And in this sound-bite world, two and a half or three minutes can feel painfully long.

NATO’s hope is to reduce the length of trailers, so they don’t give away as many plot points and all the best lines, making audience members wonder if they’ve just seen all they need to see. Though the group has no official authority to force the studios to shorten previews, theaters could decline to run ones that failed to meet their guidelines.

If NATO gets its way, it does not automatically mean that less time will elapse between when the theater goes dark and when the featured film begins. Theaters could choose to fill the same amount of time with more paid advertisements, or run 10 shorter trailers instead of eight longer ones, which some moviegoers might actually welcome.

“One time, my friends went to a bar before a movie, but I skipped it because I wanted to watch the trailers,” Daniel Mulcare, a 40-year-old professor of political science at Salem State University, said outside Loews Boston Common on a recent weekday afternoon. “I love them.”

The same day, at the Somerville Theater in Davis Square, the sentiments were similar.

“There’s something about trailers that gives me the chills,” said Chris Roberts, a 23-year-old comedian, actor, and waiter who lives in Cambridge. “I loved watching the trailers for ‘Transformers,’ but I didn’t like those movies. Even when I watch a movie on Netflix, I’m a little [ticked] off because there are no trailers.”

Producers and sisters Evelyn Brady-Watters and Monica Brady run an annual awards show called “The Golden Trailer Awards.” Jurors have included Joss Whedon and Quentin Tarantino, and this year’s awards, presented in Los Angeles in May, named the “Iron Man 3” trailer Best in Show.

“We have entered a golden age of trailers,” said Brady, a self-professed trailer nerd who says she could “stay in all night watching them.”

The first trailers, more than a century ago, actually played after movies — hence their name.

“Audiences would head out the door, so they quickly started playing before films, but the name stuck,” said film historian Eric Schaefer, associate chair of the Department of Visual and Media Arts at Emerson College. “But for the most part, trailers have not really changed in the last 70 or 80 years — it’s still introducing you to the stars, the basics of the plot, maybe a few glimpses of action or romance.”

NATO would not respond to questions regarding the potential change in its trailer policy. Jack Horner, a spokesman for Warner Bros., which distributes “The Hangover” franchise, said that the Motion Picture Association of America “is speaking on the studio’s behalf for this issue.” The MPAA, the industry group that represents Warner Bros. and the five other major Hollywood studios, also declined to comment. AMC Entertainment, which owns 346 theaters with 5,034 screens, did not respond to calls regarding the proposed change.

This is the not the only recent controversy around trailers. In 2011, a Michigan woman sued the creators of the film “Drive,” starring Ryan Gosling, for false advertising under Michigan’s Consumer Protection Act. She argued the trailer led her to believe she would be seeing a racing movie, but instead she got a slow, atmospheric, arrestingly violent art film. The suit is awaiting argument in the Michigan Court of Appeals.

The experience of previews differs between multiplexes like the Legacy Place Showcase and the nearby Dedham Community Theater. While Legacy might show seven or eight previews, lasting up to 20 minutes, smaller theaters tend to show fewer.

“We usually play no more than three, and we never exceed 10 minutes worth,” said Sarah Reynolds, manager at Dedham Community Theater. “People will sometimes come in late and assume we had 15 or 20 minutes of previews. But once they get used to it, they end up preferring it.”

Independent theaters point to it as a distinction from the multiplexes that they think their loyal moviegoers prefer.

“It’s our policy when it comes to trailers that we are audience centric,” said Denise Kasell, executive director of Coolidge Corner Theater. “We are not selling you something, we’re giving you information. I think people are smart. I do not have to scream at them over and over again.”